1. Field of the Invention
The present invention relates to an image fiber imaging apparatus comprising an image guide fiber bundle, such as a fiber scope, having a receiving end and a transmitting end, for receiving an image of an object at the receiving end and transmitting through and outputting the image at the transmitting end, an imaging device for picking up the image transmitted and outputted by the image guide fiber bundle, and a display unit for displaying the image picked up by the imaging device.
2. Description of the Related Art
In recent years, there are provided a wide variety of image fiber imaging apparatuses each of which comprising an image guide fiber bundle such as, for example, a fiber scope, having a receiving end and a transmitting end, for receiving an image of an object placed at the receiving end, and transmitting and outputting the image at the transmitting end, a solid-state imaging device for picking up the image transmitted through and outputted by the image guide fiber bundle, and a display unit for displaying the image picked up by the solid-state imaging device. The image guide fiber bundle includes a plurality of optical fibers regularly arranged in a certain manner. The image includes a plurality of image portions. The image portions collectively forming the image received by the image guide fiber bundle at the receiving end respectively enter into optical fibers collectively forming the image guide fiber bundle. More specifically, each of the optical fibers has core and clad portions. The core portion is an inner, light-guiding part of the optical fiber and the clad portion is a part surrounding the core portion. An image portion received by the image guide fiber bundle enters the core portion of an optical fiber at an angle. The fact that the refractive index of the core portion is higher than that of the clad portion leads to the fact that an image portion that enters the core portion at an angle can reflect off the boundary between the core and clad portions and propagate down the length of the optical fiber.
The core and clad portions in the regularly arranged optical fibers, however, generate dark and bright patterns in light passing through the optical fibers, thereby causing the image guide fiber bundle to output the image containing the dark and bright pattern noises at the transmitting end. The dark and bright pattern noises thus outputted will result in mesh patterns appeared in the display unit. Furthermore, the solid-state imaging device includes a plurality of light receiving elements regularly arranged in a certain manner. The regularly arranged light receiving elements interfere with the image containing the dark and bright pattern noises transmitted through and outputted at the transmitting end of the image guide fiber bundle, thereby causing Moire patterns appeared in the display unit.
Up until now, there have been proposed a wide variety of image fiber imaging apparatuses each comprising an optical lowpass filter between the image guide fiber bundle and the solid-state imaging device, in order to reduce the dark and bright patterns and Moire patterns appeared in the display unit. One typical type of such image fiber imaging apparatus is disclosed in Japanese Patent Application Laid-Open Publication No. 136813/1990.
Referring to FIG. 4 of the drawing, there is shown a conventional image fiber imaging apparatus. The conventional image fiber imaging apparatus is shown in FIG. 4 as comprising a fiber scope 12, an optical coupler 13, an optical lowpass filter 14, a solid-state imaging device 2, a camera control unit 3, and a television monitor 5. The fiber scope 12 includes a plurality of optical fibers 1. The fiber scope 12 including a plurality of optical fibers 1 is adapted to receive and transmit an image of an object. The optical lowpass filter 14 is adapted to filter the image transmitted by the fiber scope 12 by compressing high frequency components in the image. The optical coupler 13 is placed between the fiber scope 12 and the optical lowpass filter 14 and adapted to optically couple the fiber scope 12 with the optical lowpass filter 14 in an appropriate manner. The solid-state imaging device 2 is adapted to pick up and convert the image filtered by the optical lowpass filter 14 into an image signal. The camera control unit 3 and the television monitor 5 are adapted to display the image signal thus picked up and converted by the solid-state imaging device 2.
The aforesaid conventional image fiber imaging apparatus comprising an image guide fiber bundle 12, however, encounters a drawback that the conventional image fiber imaging apparatus is i to be equipped with an optical lowpass filter 14, which is expensive and large in size, in order to reduce the dark and bright patterns and Moire patterns appeared in the display unit. Furthermore, the optical lowpass filter 14 is required to be selected in accordance with the line thickness and density of the image guide fiber bundle 12.
In the conventional image fiber imaging apparatus, the image guide fiber bundle 12 is replaceable with a relay lens. The conventional fiber imaging apparatus comprising a relay lens in place of the image guide fiber bundle 12 encounters another drawback that the optical lowpass filter 14 has frequency characteristics appropriate for reducing the dark and bright patterns and Moire patterns caused by image guide fiber bundle 12 and the solid-state imaging device 2 originally equipped, thereby impossible to reduce the dark and bright patterns and Moire patterns appeared in the display unit 5 and achieve a high resolution unless the optical lowpass filter 14 is replaced or adjusted in accordance with the frequency characteristics of the relay lens newly replaced.
The present invention contemplates resolution of such problems.
It is, therefore, an object of the present invention to provide an image fiber imaging apparatus comprising an image guide fiber bundle, which achieves a high resolution, effectively reducing the dark and bright patterns and Moire patterns appeared in a display and eliminates the needs of an optical lowpass filter, which is expensive and large in size, thereby making it possible to manufacture an high-performance image fiber imaging apparatus simple in structure at a low cost.
It is another object of the present invention to provide an image fiber imaging apparatus comprising a relay lens in place of an image guide fiber bundle, which achieves a high resolution, effectively reducing the dark and bright patterns and Moire patterns appeared in a display and eliminates the needs of an optical lowpass filter, which is expensive and large in size, thereby making it possible to manufacture an high-performance image fiber imaging apparatus simple in structure at a low cost.
In accordance with a first aspect of the present invention, there is provided an image fiber imaging apparatus comprising: an image guide fiber bundle having a plurality of optical fibers, a receiving end, at which one ends of the optical fibers are arranged, and a transmitting end, at which other ends of the optical fibers are arranged, the receiving end being directed to an object to receive an image of the object, the optical fibers transmitting the image received at the receiving end to the transmitting end, the image including a plurality of image portions, each corresponding to one of the optical fibers; a solid-state imaging device arranged at the transmitting end of the image guide fiber bundle for converting the image including a plurality of image portions transmitted by the optical fibers of the image guide fiber bundle into an image signal; an electrical spatial filter for filtering the image signal converted by the solid-state imaging device to output a filtered image signal; and a display unit for displaying the filtered image signal outputted by the electrical spatial filter.
The aforesaid electrical spatial filter may include: a central image signal portion selecting unit for sequentially selecting a central image signal portion and peripheral image signal portions from among the image signal portions converted by the solid-state imaging device; a comparing unit for inputting the central image signal portion and the peripheral image signal portions selected by the central image signal portion selecting unit, respectively calculating differences of the peripheral image signal portions between the value of the central image signal portion and the values of the peripheral image signal portions, and respectively comparing the differences of the peripheral image signal portions thus calculated with a predetermined threshold value to determine peripheral image signal portions, the differences of which are less than the threshold value, as valid peripheral image signal portions and peripheral image signal portions, the differences of which are not less than the threshold value, as invalid peripheral image signal portions; and a replacing unit for calculating the average value of the valid peripheral image signal portions determined by the comparing unit, replacing the value of the central image signal portion with the average value of valid peripheral image signal portions thus calculated, and outputting the central image signal portion thus replaced as a filtered central image signal portion, whereby the central image signal portion selecting unit is operative to select a plurality of central image signal portions one after another, and the replacing unit is operative to sequentially output the central image signal portions thus replaced as filtered central image signal portions forming a filtered image signal.
Attentively, the aforesaid electrical spatial filter may include: a central image signal portion selecting unit for sequentially selecting a central image signal portion and peripheral image signal portions from among the image signal portions converted by the solid-state imaging device; a comparing unit for inputting the central image signal portion and the peripheral image signal portions selected by the central image signal portion selecting unit, respectively calculating differences of the peripheral image signal portions between the value of the central image signal portion and the values of the peripheral image signal portions, and respectively comparing the differences of the peripheral image signal portions thus calculated with a predetermined threshold value to determine peripheral image signal portions, the differences of which are greater than the threshold value, as valid peripheral image signal portions and peripheral image signal portions, the differences of which are not greater than the threshold value, as invalid peripheral image signal portions; and a replacing unit for calculating the average value of the valid peripheral image signal portions determined by the comparing unit, replacing the value of the central image signal portion with the average value of valid peripheral image signal portions thus calculated, and outputting the central image signal portion thus replaced as a filtered central image signal portion whereby the central image signal portion selecting unit is operative to select a plurality of central image signal portions one after another, and the replacing unit is operative to sequentially output the central image signal portions thus replaced as filtered central image signal portions forming a filtered image signal. The aforesaid threshold value may be adjustable in accordance with the characteristics of the solid-state imaging device and the image guide fiber bundle.
In accordance with a second aspect of the present invention, the aforesaid replacing unit may includes: an adding unit for adding all the values of the valid peripheral image signal portions determined by the comparing unit to calculate a total value of the valid peripheral image signal portions; a counting unit for counting the number of the valid peripheral image signal portions determined by the comparing unit to calculate a total number of the valid peripheral image signal portions; and a dividing unit for dividing the total value of the valid peripheral image signal portions calculated by the adding unit by the total number of the valid peripheral image signal portions calculated by the counting unit, calculating an average value of the valid peripheral image signal portions, and outputting the average value of the valid peripheral image signal portions thus calculated as a filtered central image signal portion.
The aforesaid central image signal portion selecting unit may sequentially select a central image signal portion from among the image signal portions converted by the solid-state imaging device in accordance with an operating instruction.
In accordance with a third aspect of the present invention, the aforesaid electrical spatial filter may further includes an object area determining unit for determining an object area to be displayed in the display unit, the central image signal portion selecting unit is operative to sequentially select a central image signal portion from among the image signal portions converted by the solid-state imaging device in accordance with the object area determined by the object area determining unit.
In accordance with a fourth aspect of the present invention, the aforesaid image guide fiber bundle is replaceable with a relay lens for receiving an image of an object, and transmitting the image including a plurality of image portions, and the solid-state imaging device is operative to convert the image including a plurality of image portions transmitted by the relay lens.